1. Field of the Invention
The invention relates in general to temperature measurement of a radiating body. More particularly, this invention relates to apparatuses and a method that utilize the principle of the alexandrite effect to measure temperature of any radiating body, such as, but not limited to, blackbody, graybody, plasma, electric arc, and combustion. The invented apparatuses are particularly advantageous to measure high to ultrahigh temperature of radiating bodies with spectral line emissions, such as plasma and electric arc.
2. Description of the Related Art
Pyrometers are known and commercially available for non-contacting temperature measurement of radiating bodies. Pyrometers can be particularly helpful in different contexts. First, they can be used when the target is located in a remote location. Pyrometers can also be helpful when the temperature or environment near the target is too hostile or severe for temperature measurement by other, more conventional, means. Finally, pyrometers are useful when temperature measurement by contact may alter the target temperature.
Conventional pyrometry methods include the two-color method, the disappearing filament method, the total radiation method, the photoelectric method, the two-wavelength method and the multi-wavelength method. The two and multi-wavelength methods are usually used to measure temperature by measuring the radiation of a radiating body in the infrared range, as described in U.S. Pat. No. 4,142,417 to Cashdollar, U.S. Pat. No. 4,880,314 to Kienitz, and U.S. Pat. No. 5,326,171 to Ng. U.S. Pat. No. 5,772,323 to Felice extends the multi-wavelength measurement into the visible range. In U.S. Pat. No. 6,109,783, Chen discloses a pyrometer that measures the temperature in hazardous environments using specially designed probes.
Although conventional pyrometers can measure the temperature of blackbody and graybody matter, they cannot measure the temperature of a radiating body with spectral line emission. A spectral line is a bright line found in the spectrum of some radiant source, and occurs when atomic, molecular, or gas excitation exists. Examples of radiating bodies that emit spectral lines include plasmas and electric arcs. The spectral lines in the spectral power distributions of these radiating bodies make conventional methods such as the multi-wavelength method void.
Special methods have been implemented to determine the temperature of gas and plasma over 5000° C. The methods include the absolute intensity method, the line ratio method, the relative intensity method, and the Rayleigh scattering method. These methods are inadequate, however. The absolute intensity method is not accurate, with error in the range of 10% to 20%. The line radio method, relative intensity method and the Rayleigh scattering method are expensive to implement, are only reasonably accurate, and are not readily available to consumers.
Therefore, the need arises for an apparatus and method capable of measuring radiating bodies of blackbody and graybody matter with continuous spectral power distribution, as well as plasma and electric arcs with spectral line emissions. The apparatus must be accurate, relatively inexpensive, and readily available to consumers.